The invention relates to a circular rotary cutting tool used especially for cutting products or articles made of steel and other materials, such as, for example, wood. It relates more specifically to a rotary cutting tool of the type in question, produced by means of two different materials.
Typically, slitting saws to which the invention mainly relates are one-piece. They possess:
at their centre, a driving hub having a bore and equipped with driving holes to allow interaction with a drive shaft,
and a peripheral ring comprising the actual cutting zone, the assembly as a whole forming one and the same entity usually produced from so-called "high-speed" steel.
The peripheral ring of slitting saws is toothed. In general terms, these teeth have a spacing and hardness which can vary from one slitting saw to another according to its use and its rotational speed.
In a known way, the body has some clearance, typically of the order of 1 to 2%, intended to allow the discharge of chips of cut material and the lubrication of the cutting zone.
Such one-piece tools have disadvantages by virtue of their very structure and design. First of all, only the operational part of the peripheral ring has to have a suitable hardness. Now, in view of the design, the entire slitting saw is produced with the same alloy, thus entailing not only an extra cost, but a heavy tool, and moreover, necessitating periodic resharpening of the actual cutting zone. Now this resharpening is usually sub-contracted. That implies a large and therefore costly stock requiring relatively strict management. Furthermore, these successive resharpening operations result in a loss of cutting capacity of the tool, in view of the cut made within the peripheral ring itself in order to obtain a form close to that of a new tool.
Besides, in the event of a shock, the tool as a whole is embrittled, often making it unsuitable for subsequent cutting operations.
Finally, because of the solid one-piece nature of this tool, it proves very noisy during cutting, making the operators' work arduous.
There was then provided a cutting tool which is first and foremost light, performs the same functions as the rotary cutting tools known hitherto and makes it possible to damp some of the vibrations inherent in the actual cutting and which, because of its cost price, makes it unnecessary to carry out successive periodic resharpening operations and thereby simplifies the management of the stock of cutting tools. For this purpose, the central body of the cutting tool, of generally circular shape and comprising the hub for driving the tool, is produced from a synthetic material, to which the peripheral ring comprising the actual cutting zone is fastened. Such a tool was described, for example, in the document DE-U-8811470.
Now although the tool produced in this way achieves a technical advance, especially with regard to the reduction of vibrations during cutting, and an undeniable weight saving, nevertheless the method of fastening the peripheral ring to the central body has hitherto proved unsatisfactory. In fact, the fastening can be carried out in various ways. First of all, the peripheral ring can simply be bonded adhesively to the central body. It was soon seen that this method of fastening was inadequate in view of the torque generated in the region of the ring by the central body.
It was then proposed to duplicate this method of fastening with the fitting of rivets or bolts passing through the peripheral ring and the central body in the region of the contact zones. However, this entails at least one additional step of machining the ring and central body and of fitting the said rivets and/or bolts which is incompatible with the industrial production of such tools.
It was then proposed to bond the peripheral ring adhesively to a T-shaped support embeddable in the central body. This technique is unsatisfactory because the torque of the drive shaft is inappropriately transferred to the peripheral ring, this occurring even if orifices capable of being filled with the resin forming the central body are provided in the said support.
Finally, it was proposed to equip the support of the peripheral ring with dovetailed recesses intended to be filled with the resin forming the central body of the tool. Now this method of fastening is completely ruled out because, during the solidification of the resin, there is usually a shrinkage of the plastic which is adversely affected and even prevented by the special dovetail shape of the recesses of the support. Thus, the mechanical stresses associated with the shrinkage of the plastic are exerted preferentially in a preferred direction and not isotropically, thereby inducing a residual warping of the cutting tool which makes it completely unsuitable for use.